1. Field of the Invention
The present invention generally relates to an image forming apparatus such as an inkjet recording apparatus, and more particularly to a technique of correcting a recording position of image data in an image forming apparatus having the recording head capable of performing bi-directional scanning in the main-scanning direction to form the image data.
2. Description of the Related Art
Generally, there has been known an image forming apparatus having its image forming section employing an electrophotographic image forming method such as a printer, a facsimile machine, a copier, or a multifunction peripheral having such functions. Some image forming apparatuses include the image forming section employing an inkjet printing method by which an image is formed (terms recorded, printed, imaged, typed may be used as synonyms of the term formed) by adhering the droplets of a recording liquid (ink) (hereinafter may be referred to as ink droplets) to a recording medium to be printed (hereinafter may be referred to as a sheet, the material of the sheet is not limited, and a recording medium, transfer material and the like may be used as synonyms) by using a recording head constituted by an ink liquid ejection head for ejecting the droplets of recording ink liquid.
In such an image forming apparatus employing the inkjet printing method, an image is recorded by scanning a carriage on which the recording head is mounted in both the forward direction and the backward direction along the main-scanning direction and intermittently feeding the recording medium in the sub-scanning direction. More specifically, when the carriage having the recording head is scanned in both forward and backward directions, an encoder scale disposed in the main scanning direction is detected by an optical sensor so that the positional information of the carriage is obtained; the ejection timing of the recording head based on the obtained positional information is generated; and ink is ejected from the recording head at the generated ejection timings, so that the image is recorded on the recording medium.
However, there may arise a problem that when an image is formed by scanning in both forward and backward directions in the main-scanning direction (i.e., in bi-directional printing), the recorded positions may be shifted (displaced) due to the shifted positions between the dots formed in the forward scanning and the dots formed in the backward scanning.
To overcome the problem, Japanese Patent Application Publication No. 2005-335343 proposes a technique in which the shift amount of ink landing positions in the sub-scanning direction is corrected by detecting the shift amount in the sub-scanning direction between the forward direction and the backward direction along the sub-scanning direction and adjusting the feeding amount of the recording medium.
On the other hand, Japanese Patent Application Publication No. 2000-296609 proposes a technique in which the shift of ink landing positions in the main-scanning direction is corrected by detecting the shift amount in the main-scanning direction between the forward direction and the backward direction in the main-scanning direction and adjusting the driving timing to the recording head.
However, in the Japanese Patent Application Publication Nos. 2000-296609 and 2000-296609, the positional shift amount is detected in only one of the main-scanning direction and the sub-scanning direction. Therefore, the correction performed may not be accurate enough.